Some beverage products rely on bubble formation to achieve taste characteristics and/or visual appeal. For example, carbonated beverage products naturally generate carbon dioxide bubbles activated by the pressure change when a container is opened and/or during pouring; however, other products such as stout beer rely on dissolved nitrogen to come out of solution and create a distinctive taste and fine creamy “head” in a poured glass. The formation of bubbles in a stout beer is a far less naturally active process than a carbonated product and, as such, an additional nucleation means is required. Stout beers of this type contain a mixture of nitrogen and carbon dioxide but, at the serving temperature, the amount of dissolved carbon dioxide is below its equilibrium level so there is no tendency for it to come out of solution.
The characteristic experience of stout beer, where bubble formation needs to be initiated during pour to form a creamy, white head, and its smoothness of taste (as opposed to a more acidic taste influenced by carbonation) is currently produced by one of three methods: (1) flow through a restrictor plate in a draught dispenser; (2) cavitation of stout in the glass by way of an ultrasonic unit; or (3) injection of gas/liquid via a “widget” in a bottle or can. These methods are proven effective, but all require systems that are not easily incorporated into packaging. For example, production of cans to emulate the draught effect via a widget requires specialized capital equipment, as well as economic losses associated with the slower canning speeds compared to traditional canned beverages. The canned stout provided for use with ultrasonic systems is the same as the product supplied in kegs but obviously requires additional apparatus (i.e. the ultrasonic unit) to be operated by a barman or at home by a consumer.
Nucleation and growth of carbon dioxide bubbles in beverages is well documented (see (1) Jones, S. F.; Evans, G. M.; Galvin, K. P. “Bubble nucleation from gas cavities—a review,” Adv. Coll. Inter. Sci. 1999, 80, 27-50; (2) Jones, S. F.; Evans, G. M.; Galvin, K. P. “The cycle of bubble production from a gas cavity in a supersaturated solution,” Adv. Coll. Inter. Sci. 1999, 80, 51-84). It has also been noted that cellulose fibres present in glasses promote carbon dioxide bubble growth and, as such, the possibility of providing a special surface on a wall inside a container to encourage bubble nucleation and growth has been proposed for nitrogen supersaturated products such as stout (Lee, W. T.; McKechnie, J. S.; Devereux, M. “Bubble nucleation in stout beers,” Phys. Rev. E, 2011, 83, 051609).
The research further concludes that Type 4 nucleation (as defined by Jones et al) occurs at a lower degree of supersaturation than other types of heterogeneous nucleation. Type 4 nucleation occurs from pre-existing nuclei, e.g. trapped gas, which is present on a surface.
The concept of using structured cellulose surfaces to enhance bubble nucleation and growth is supported by experimental studies in stout beer. Cellulose fibres are multi-scale structures comprised of hollow tubes with an inner lumen diameter of 1-10 μm and multilayer walls consisting of densely packed microfibrils. However, while cellulose shows efficacy, it is not an ideal material for a container surface coating both due to the challenges of incorporating it into a coating and issues with its influence on the beer itself.
The patent literature suggests various systems for encouraging nucleation. For example, FR2531891 describes making nucleation sites using a laser beam to create a visual effect, like a logo, in the glass. Such a system is at a scale similar to that described above. Similarly, GB2420961A describes laser or sonic etching on a plastic and polycarbonate container.
US2002000678A1, US2010104697A1 and GB2136679A describe forming patterns of nucleation sites, e.g. on the base of a glass. Some of the prior art ensures these patterns are able to reach the top of the liquid. However, there is no description for how to better nucleate gas nor the materials used. Nucleation sites are made at the microscale.
JP62109859 describes a container coating for scavenging oxygen down to scales of 0.01 micrometers thick.
WO9412083A1 describes an etching process and tools for use, but nothing about materials, dimension of sites etc.
WO9500057A1, although mentioning CO2 and mixed gas CO2/N2, is concerned with a manufacturing process of gas nucleation drinking glasses (e.g. pre-treatment, annealing process, temperature of baking, etc).